1. Field of the Invention
The present invention generally relates to a common rail comprising a block rail in an accumulator fuel injecting system of a diesel internal combustion engine.
2. Description of the Prior Arts
Conventionally, as a common rail of this kind, for example, as shown in FIG. 12, there has been known a common rail of the type which is structured such that a branch hole 11-2 communicating with an communication passage 11-1 of a block rail 11 and having a pressure receiving seat surface 11-3 open to an outer portion is punched in a bottom portion 12-2 of a plurality of connecting hole portions 11-4 provided in a peripheral wall portion of the block rail 11 having a rectangular cross section in an axial direction at an interval, a pressing seat surface 12-3 constituted by a connecting head portion 12-2 of a branch pipe 12 end is brought into contact with and engaged with the pressure receiving seat surface 11-3 of the block rail 11 end, and a fastening external screw nut 13 previously assembled in the branch pipe end is meshed with the connecting hole portion 11-4, thereby fastening and connecting together with pressing under a neck of the connecting head portion 12-2. In the drawing, reference numeral 12-1 denotes a flow passage of the branch pipe 12. In this case, the cross sectional shape of the block rail is not limited to a rectangular shape, and various kinds of shapes such as a triangular shape and a trapezoidal shape can be employed.
However, in the case of the conventional common rail structured such that the branch hole 11-2 is provided in the connecting hole portion 11-4 disposed in the block rail 11, a great tensional force is generated in an inner peripheral edge portion P of a lower end of the branch hole 11-2 due to a repeating high internal pressure within the block rail 11 and an axial force applied to the pressure receiving seat surface 11-3 together with a pressing of the connecting head portion 12-2 in the branch pipe 12, so that a crack is easily generated from the inner peripheral edge portion P of the lower end and there is a possibility of causing a leak.